Computer systems provide techniques for users to communicate with each other. One example system may make use of an Internet Protocol (“IP”) Multimedia Subsystem (“IMS”) core (e.g., as standardized by the Third Generation Partnership Project (“3GPP”)), which may facilitate the use of IP protocols for communications, such as telephony, fax, e-mail, voice over IP (“VoIP”), instant messaging, video messaging, and/or other services. Some communication standards (such as the Rich Communications Suite (“RCS”), developed by the Global System for Mobile Communications Association (“GSMA”)) may provide enhanced communications features, such as address books, presence information, file transfer, syncing, and/or other features.